Apparatus and method for frame rate up conversion

ABSTRACT

An apparatus for frame rate up conversion comprises a motion-compensated frame rate converter, a primitive frame rate converter and a determination circuit. The determination circuit designates either the motion-compensated frame rate converter or the primitive frame rate converter to output an interpolated frame according to an index that estimates an output quality of the motion-compensated frame rate converter.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to video processing, and more particularlyrelates to an apparatus and a method for frame rate up conversion.

2. Description of the Related Art

To support high frame rate display, it may need to convert a receivedlow frame rate video signals, e.g. 60 Hz, into a high frame rate videosignal, e.g. 120 Hz.

In frame rate up conversion (FRUC), interpolated frames are createdusing received frames as references. Currently, frame interpolation maybe obtained based on motion vectors of the received frames such thatmoving objects within the interpolated frame may be correctlypositioned.

Although motion-compensated frame rate up conversion (MC-FRUC) offerssome advantages in most cases, it also suffers artifacts when motionestimation is incorrect. In particular, motion estimation is never easywhen the received frames are complex or speedy.

Accordingly, there is a need to determine whether the motion-compensatedframe rate up conversion is quality or not. Furthermore, when themotion-compensated frame rate up conversion is not quality enough,another primitive frame rate up conversion, such as frame averaging orframe repetition, can be used as a substitute.

SUMMARY OF THE INVENTION

An objective of the present invention is to provide an apparatus and amethod for frame rate up conversion that displays a high-frame-ratevideo signal in an improved way. By determining whether themotion-compensated frame rate converter is quality or not, the apparatusfor frame rate up conversion can selectively use a motion-compensatedframe rate converter or a primitive frame rate converter so as toprovide superior output quality.

In order to achieve the objective, the present invention discloses anapparatus for frame rate up conversion. The apparatus comprises amotion-compensated frame rate converter, a primitive frame rateconverter and determination circuit. The determination circuitdesignates either the motion-compensated frame rate converter or theprimitive frame rate converter to output an interpolated frame accordingto an index that evaluates the output quality of the motion-compensatedframe rate converter.

In another embodiment, the present invention discloses a method forframe rate up conversion. First, an index evaluating the output qualityof motion-compensated frame rate conversion is calculated. Aninterpolated frame is outputted by selecting one of themotion-compensated frame rate conversion and a primitive frame rateconversion according to the index.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described according to the appended drawings inwhich:

FIG. 1 shows a function block diagram of an apparatus for frame rate upconversion in accordance with the present invention;

FIG. 2 shows a flow chart of a method for frame rate up conversion inaccordance with the present invention;

FIG. 3 shows a flow chart exemplifying how to counting the frequency ofdisqualified motion vectors in edging regions of a motion-compensatedinterpolated frame output by the motion-compensated frame rate converter11 and assign a quality flag to the motion-compensated interpolatedframe based on the frequency in accordance with the present invention;and

FIG. 4 shows a diagram explaining how to accumulate a grade based onquality flags for a succession of motion-compensated interpolated framesin accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a function block diagram of an apparatus 10 for frame rateup conversion in accordance with the present invention. The apparatus 10comprises a motion-compensated frame rate converter 11, a primitiveframe rate converter 12 and determination circuit 13. The determinationcircuit 13 can designate either the motion-compensated frame rateconverter 11 or the primitive frame rate converter 12 to output aninterpolated frame according to an index that evaluates the outputquality of the motion-compensated frame rate converter 11. The index maybe obtained by counting the frequency of disqualified motion vectors inedging regions of a motion-compensated interpolated frame output by themotion-compensated frame rate converter 11, assigning a quality flag ofthe motion-compensated interpolated frame based on the frequency, andaccumulating a grade as the index based on a plurality of quality flagsfor a succession of motion-compensated interpolated frames.

FIG. 2 shows a flow chart of a method for frame rate up conversion inaccordance with the present invention. Referring to Step 21, an indexthat evaluates the output quality of the motion-compensated frame rateconversion is calculated. The index may be obtained by calculating thefrequency of disqualified motion vectors in edging regions of amotion-compensated interpolated frame output by the motion-compensatedframe rate conversion, assigning a quality flag to themotion-compensated interpolated frame based on the frequency, andaccumulating a grade as the index based on a plurality of quality flagsfor a succession of motion-compensated interpolated frames. As shown inStep 22, the conversion method determines whether the output quality ofthe motion-compensated frame rate conversion meets an acceptable levelaccording to the index. That is, the output quality of themotion-compensated frame rate conversion is evaluated to be in anacceptable state or in a disqualified state. Afterward, as shown in StepS23, either the motion-compensated frame rate conversion or a primitiveframe rate conversion that is likely to implement frame averaging orframe repetition is adaptively designated to output a more adequateinterpolated frame based on the determination.

FIG. 3 shows a flow chart exemplifying how to count the frequency ofdisqualified motion vectors in edging regions of a motion-compensatedinterpolated frame output by the motion-compensated frame rateconversion and assign a quality flag to the motion-compensatedinterpolated frame based on the frequency in accordance with the presentinvention. As shown in Step 31, the frequency of disqualified motionvectors in edging regions of a motion-compensated interpolated frameoutput by the motion-compensated frame rate conversion may be obtainedby dividing the number CO_(b) of disqualified motion vectors withinedging regions of the motion-compensated interpolated frame output bythe motion-compensated frame rate conversion by the number CO_(e) of allmotion vectors in the same regions. As an example, a motion vector maybe evaluated as a disqualified motion vector if the sum of absolutedifference (SAD) value between corresponding macroblocks in themotion-compensated interpolated frame and its reference frame is largerthan a threshold. Moreover, edging regions of the motion-compensatedinterpolated frame may be also detected by known edge detectiontechniques, which will not be described herein for simplicity. When thefrequency of disqualified motion vectors is smaller than a first level,a “G (good)” quality flag is assigned to the motion-compensatedinterpolated frame, as shown in Steps 32 and 34. For example, if thefrequency of disqualified motion vectors is smaller than 60%representing a maximum tolerable frequency, the quality of themotion-compensated interpolated frame is acceptable and a “G (good)”quality flag is assigned thereto. When the frequency of disqualifiedmotion vectors is larger than a second level, a “B (bad)” qualify flagis assigned to the motion-compensated interpolated frame, as shown inSteps 33 and 35. For example, if the frequency of disqualified motionvectors is larger than 70% representing a minimum intolerable frequency,the quality of the motion-compensated interpolated frame is intolerableand a “B (bad)” quality flag is assigned thereto. As shown in Step 36,when the frequency of disqualified motion vectors happens to be lowerthan the maximum tolerable frequency and higher than the minimumintolerable frequency, the quality of the motion-compensatedinterpolated frame is hard to decide and a quality flag being the sameas that assigned to the preceding motion-compensated interpolated frameis assigned thereto.

FIG. 4 shows a diagram explaining how to accumulate a grade as the indexbased on quality flags for a succession of motion-compensatedinterpolated frames. Suppose frames f1-f16 are successive interpolatedframes output by either the motion-compensated frame rate conversion ora primitive frame rate conversion that is likely to implement framerepetition or frame averaging. Quality flags for the successivemotion-compensated interpolated frames output by the motion-compensatedframe rate conversion may be recorded.

The index that evaluates the output quality of the motion-compensatedframe rate conversion may be obtained by accumulating a grade, e.g.ranging from grade 0 to grade 8, as the index based on the qualityflags. If the grade during the first interpolated frame f1 isinitialized at the middle, grade 4 in this case, and an acceptable levelof the motion-compensated frame rate conversion is defined, for example,between grade 5 and grade 6. When the accumulated grade is increased tobe over the acceptable level, the corresponding interpolated frame canbe output by the motion-compensated frame rate conversion. Conversely,the corresponding interpolated frame can be output by the primitiveframe rate conversion when the accumulated grade is decreased to beunder the acceptable level.

Furthermore, in one embodiment, if the motion-compensated interpolatedframe is assigned to a “B (bad)” quality flag, the accumulated grade maybe decreased by a certain value. As shown in FIG. 4, the accumulatedgrade during the second interpolated frame f2 is downgraded to grade 2from grade 4 during the first interpolated frame f1. Conversely, theaccumulated grade is increased by a certain value if themotion-compensated interpolated frame is assigned to a “G (good)”quality flag. As shown in FIG. 4, the accumulated grade during the thirdinterpolated frame f3 is upgraded to grade 3 from grade 2 during thesecond interpolated frame f2. Further, the accumulated grade may belimited in a range, for example, between grade 8 and grade 0. Therefore,if the accumulated grade reaches grade 8, the accumulated grade willremain unchanged at grade 8, even though the next motion-compensatedinterpolated frame is assigned to a “G (good)” quality flag. Similarly,if the accumulated grade falls to grade 0, the accumulated grade willalso remain unchanged at grade 0, even though the nextmotion-compensated interpolated frame is assigned to a “B (bad)” qualityflag.

Using the accumulated grade as the index, when the accumulated gradeduring an interpolated frame such as the sixth interpolated frame f6 isincreased from grade 5 to grade 6 being above the acceptable level, theinterpolated frame can be output by the motion-compensated frame rateconversion. Similarly, the interpolated frame can be output by theprimitive frame rate conversion when the accumulated grade during theinterpolated frame such the twelfth interpolated frame f12 is decreasedfrom grade 6 to grade 4 being under the acceptable level.

Also, it should be noted the decreasing step for the grade accumulationis preferably designed to be larger than the increasing step, such thatthe interpolated frame may be quickly switched and output by theprimitive frame rate conversion when the output quality of themotion-compensated frame rate conversion is not quality enough.

The above-described embodiments of the present invention are intended tobe illustrative only. Numerous alternative embodiments may be devised bypersons skilled in the art without departing from the scope of thefollowing claims.

1. An apparatus for frame rate up conversion, comprising: amotion-compensated frame rate converter performing motion-compensatedinterpolation; a primitive frame rate converter performing a primitiveinterpolation; and a determination circuit adaptively designating eitherthe motion-compensated frame rate converter or the primitive frame rateconverter to output an interpolated frame.
 2. The apparatus for framerate up conversion of claim 1, wherein the determination circuit outputsthe interpolated frame according to an index that evaluates the outputquality of the motion-compensated frame rate converter.
 3. The apparatusfor frame rate up conversion of claim 2, wherein the index is obtainedby counting the frequency of disqualified motion vectors in edgingregions of a motion-compensated interpolated frame output by themotion-compensated frame rate converter, assigning a quality flag of themotion-compensated interpolated frame according to the frequency, andaccumulating a grade as the index based on a plurality of quality flagsfor a succession of motion-compensated interpolated frames.
 4. Theapparatus for frame rate up conversion of claim 3, wherein the frequencyof disqualified motion vectors is obtained by dividing the number ofdisqualified motion vectors in the edging regions by the number of allmotion vectors in the same regions, and the disqualified motion vectorsare sustained if the sum of absolute difference (SAD) value betweencorresponding macroblocks in the motion-compensated interpolated frameand its reference frame is larger than a threshold.
 5. The apparatus forframe rate up conversion of claim 3, wherein the quality flag isdesignate as good if the frequency is lower than a maximum tolerablefrequency, designate as bad if the frequency is higher than a minimumintolerable frequency, and remains the same as that of a precedingmotion-compensated interpolated frame if the frequency is between themaximum tolerable frequency and the minimum intolerable frequency. 6.The apparatus for frame rate up conversion of claim 5, wherein the gradeis increased if the corresponding quality flag is designated as good ordecreased if the corresponding quality flag is designated as bad.
 7. Theapparatus for frame rate up conversion of claim 6, wherein the grade isincreased by a first step if the corresponding quality flag isdesignated as good or decreased by a second step larger than the firststep if the corresponding quality flag is designated as bad.
 8. Theapparatus for frame rate up conversion of claim 1, wherein the primitiveframe rate converter is provide to implement frame repetition or frameaveraging.
 9. A method for frame rate up conversion, comprising thesteps of: calculating an index that evaluates the quality ofmotion-compensated frame rate conversion; determining whether themotion-compensated frame rate conversion meets an acceptable levelaccording to the index; and designating either the motion-compensatedframe rate conversion or a primitive frame rate conversion to output aninterpolated frame based on the determination.
 10. The method for framerate up conversion of claim 9, wherein the index is obtained by countingthe frequency of disqualified motion vectors in edging regions of amotion-compensated interpolated frame output by the motion-compensatedframe rate conversion, assigning a quality flag of themotion-compensated interpolated frame according to the frequency, andaccumulating a grade as the index based on a plurality of quality flagsfor a succession of motion-compensated interpolated frames
 11. Themethod for frame rate up conversion of claim 10, wherein the frequencyof disqualified motion vectors is obtained by dividing the number ofdisqualified motion vectors in the edging regions by the number of allmotion vectors in the same regions, and the disqualified motion vectorsare sustained if the sum of absolute difference (SAD) values betweencorresponding macroblocks in the motion-compensated interpolated frameand its reference frame is larger than a threshold.
 12. The method forframe rate up conversion of claim 10, wherein the quality flag isdesignated as good if the frequency is lower than a maximum tolerablefrequency, designated as bad if the frequency is higher than a minimumintolerable frequency, and remains the same as that of a precedingmotion-compensated interpolated frame if the frequency is between themaximum tolerable frequency and the minimum intolerable frequency. 13.The method for frame rate up conversion of claim 12, wherein the gradeis increased if the corresponding quality flag is designated as good ordecreased if the corresponding quality flag is designated as bad. 14.The method for frame rate up conversion of claim 13, wherein the gradeis increased by a first step if the corresponding quality flag isdesignated as good or decreased by a second step larger than the firststep if the corresponding quality flag is designated as bad.
 15. Themethod for frame rate up conversion of claim 9, wherein the primitiveframe rate conversion is provided to implement frame repetition or frameaveraging.